New transistors: An alternative to silicon and better than graphene

January 30, 2011, Ecole Polytechnique Federale de Lausanne

This is a digital model showing how molybdenite can be integrated into a transistor. Credit: Credit: EPFL

Smaller and more energy-efficient electronic chips could be made using molybdenite. In an article appearing online January 30 in the journal Nature Nanotechnology, EPFL's Laboratory of Nanoscale Electronics and Structures (LANES) publishes a study showing that this material has distinct advantages over traditional silicon or graphene for use in electronics applications.

A discovery made at EPFL could play an important role in electronics, allowing us to make transistors that are smaller and more energy efficient. Research carried out in the Laboratory of Nanoscale Electronics and Structures (LANES) has revealed that molybdenite, or MoS2, is a very effective semiconductor. This mineral, which is abundant in nature, is often used as an element in steel alloys or as an additive in lubricants. But it had not yet been extensively studied for use in electronics.

100,000 times less energy

"It's a two-dimensional material, very thin and easy to use in nanotechnology. It has real potential in the fabrication of very small transistors, light-emitting diodes (LEDs) and solar cells," says EPFL Professor Andras Kis, whose LANES colleagues M. Radisavljevic, Prof. Radenovic et M. Brivio worked with him on the study. He compares its advantages with two other materials: silicon, currently the primary component used in electronic and computer chips, and graphene, whose discovery in 2004 earned University of Manchester physicists Andre Geim and Konstantin Novoselov the 2010 Nobel Prize in Physics.

One of molybdenite's advantages is that it is less voluminous than silicon, which is a three-dimensional material. "In a 0.65-nanometer-thick sheet of MoS2, the electrons can move around as easily as in a 2-nanometer-thick sheet of silicon," explains Kis. "But it's not currently possible to fabricate a sheet of silicon as thin as a monolayer sheet of MoS2." Another advantage of molybdenite is that it can be used to make transistors that consume 100,000 times less energy in standby state than traditional silicon transistors. A semi-conductor with a "gap" must be used to turn a transistor on and off, and molybdenite's 1.8 electron-volt gap is ideal for this purpose.

Better than graphene

In solid-state physics, band theory is a way of representing the energy of electrons in a given material. In semi-conductors, electron-free spaces exist between these bands, the so-called "band gaps." If the gap is not too small or too large, certain electrons can hop across the gap. It thus offers a greater level of control over the electrical behavior of the material, which can be turned on and off easily.

The existence of this gap in molybdenite also gives it an advantage over graphene. Considered today by many scientists as the electronics material of the future, the "semi-metal" graphene doesn't have a gap, and it is very difficult to artificially reproduce one in the material.

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Oh, don't be so pessimistic. Just think of all the possibilities for the applications it could spawn. How about variable reactance circuits? It could be the stepping stone to smaller logic circuits for miniature, insect size robots. The power savings from these circuits could reduce the amount of stored power. If they can make electric motors out of this stuff, just think of how much longer the robots missions could last. If the parts have a low friction surface, maybe they can be utilized in moving parts that have multiple functions; therefor saving even more space and materials.

early radio receivers used sulfide crystals (FeS ,PbS ect) as a diode so it is odd that the use of metal sulfide in transistors has not been tried before now. With a band gap potential of 1.8 volts it may be possible to make high voltage power transistors for radio tranmitters and power converters.

is odd that the use of metal sulfide in transistors has not been tried before now

Not so odd. It is used as a lubricant. It doesn't stick to much. Making it stay in a transistor is going to be tricky. At a guess it is used for lubrication for the same reasons graphite is. Graphite forms thin layers that don't stick to each other. Getting either material to stray in place is going to part of what needs to be developed.

they are past the phase of figuring out how to create a band gap in graphene -- you got bigger issues -- it's just not well understood by enough people -- and there is no industrial fabrication process yet ---

once there is at least on factory for industrial fabrication of graphene then and only then will you see it hit computer chips. But there is no need because current technology will last until 2014 -- and somewhere around 2016 we will start to see the new phase of electronics that the future is going to use. -- its just too early to know what the industry is doing.

Long time for all this to have a commercial impact. Why?: As "El Nose" stated above, this technology needs until 2016 to get all process ready. And I think the companies who invest in all the technology that is moving around right now, want their investments back before going into another technology. Before that, we´ll have to wait. It is a pity. I read a lot of ground braking news for science, incredible machines and computers, but they take SO long to get to our hands.

It seems much more likely to me that molybdenite will move into production first, because fabrication would be much more conventional for it, but it also seems likely that with the lower temp carbon nanotubes, carbon wiring on chip will probably follow it closely.

The illustration shows a hafnium oxide-insulated gate field-effect transistor using molybdenum sulfide as the channel material. If it performs as described and is as easy to fabricate as silicon devices, this technology could quickly make its way into production. One of the most interesting applications, however, might be in solar cells for energy production, where its band gap and high electron mobility might offer higher efficiencies than silicon.

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